1. Field of the Invention
The present invention relates to an improved water seal drum used in gas flow paths. This drum is particularly useful as a device for preventing backfire of a flare stack.
2. State of the Art
In the process of passing a gas through a water seal drum in a gas flow path, if the dispersion of the gas becomes uneven or the gas bubbles are too large, a strong sloshing of the water level occurs in a seal drum. At an increased gas flow rate, the gas blows up water into the space upper the water level in the drum. As a result, the flow of gas in a gas discharging pipe of the water seal drum becomes a pulsating flow. It is necessary to prevent such phenomenon as much as possible.
For example, a water seal drum is used in the path of the gas being transferred to a flare stack for burning. Where the function of the water seal drum is dissatisfactory, there will be a "breathing" or "growing and diminishing" of the flare, which causes the emission of a discontinuous sound and annoys the people living in the surrounding district.
In general, a water seal drum essentially comprises a vessel containing the seal water, a gas introducing pipe extending downward from the upper part of the vessel and having a lower end which opens beneath the water level, and a gas discharging pipe at the top of the vessel. Usually, the lower open end of the gas introducing pipe is serration cut or has many slits in the axial direction so that the gas may bubble up in the water.
On studying the mechanism of the water seal, we observed the following phenomena:
In the case of a relatively low gas flow rate, the bubbles conglomerate, grow large and rise up discontinuously. As a result, the water level is apt to rise up and down at the center of the vessel where the gas introducing pipe is located. When the gas flow rate is intermediate, sloshing of the water level occurs. At a further increased gas flow rate, partial blow off of water drops occur discontinuously. In this case, the flow of gas in the gas discharging pipe becomes a pulsating flow resulting in the breathing of the flame at the flare stack and the emission of a discontinuous sound. If the blowing off becomes more serious, it may even develop into an oscillation of the seal water, the level of which rises and falls within the gas discharging pipe. This phenonenon must, of course, be avoided in a water seal drum.
In order to solve such a problem in the water seal drum, it has been found effective to disperse the gas in the form of bubbles, as small as possible, uniformly into the water so as to minimize sloshing motion of the water surface. Thus, there have been various efforts made to effect the improvements. For instance, it has been proposed to provide numerous holes in the gas introducing pipe in the portion beneath the water level, or to arrange a perforated plate extending radially at the lower end of the pipe so that the gas may be dispersed through the holes or perforations. These improvements are, however, still unsatisfactory.